1. Field of the Invention
The present invention relates to dielectric ceramic compositions having enhanced dielectric constants and ceramic electronic components using the dielectric ceramic compositions as dielectric layers.
2. Description of the Related Art
In recent years, the performance of electronic components has been significantly improved. In particular, computers to support the information-intensive society and information processing units such as mobile communication terminals are moving toward higher information processing speeds and more compact and versatile devices. Improvements in information processing devices are achieved by high integration densities, high processing speeds, and the advanced capabilities of semiconductor devices such as VLSI and ULSI. Such high-speed, high-capacity semiconductor devices, however, do not always perform optimally because substrates for connecting devices generate signal delays, cross-talk, impedance mismatch, and noise due to fluctuations in the supplied voltage.
A multichip module (MCM) including a plurality of semiconductor devices on a ceramic substrate is used in practice as a substrate for performing high-speed and high-performance information processing. Among MCMs, a ceramic multi-layer substrate including a three-dimensionally arranged conductor pattern is useful for increasing the mounting density of semiconductor devices and for performing making electrical connections.
Alumina has been conventionally used as an insulating material for such a ceramic multi-layer substrate. Since alumina requires a sintering temperature as high as 1,500xc2x0 C., a high-melting-point metal, such as tungsten and molybdenum, must be used as a conductive material for one-stage sintering. Sintering is generally performed in a reducing atmosphere to prevent oxidation of the high-melting-point metal. Moreover, the high-melting-point metal has a large specific resistance. Thus, high-frequency characteristics of the ceramic multi-layer substrate are limited.
In addition, alumina generally has a large specific dielectric constant of approximately 10. This may cause signal delays during high-speed operation of the semiconductor device. Since alumina has a large coefficient of thermal expansion compared to silicon, which is often used in semiconductor devices, reliability may be reduced due to thermal cycling.
In order to solve these problems, low-temperature sinterable ceramic materials which are composite materials of ceramic components and glass components are being intensively studied and ceramic multi-layer substrates using these materials are being developed. The low-temperature sinterable ceramic materials contain ceramic components as matrices and glass components as sintering auxiliaries, and have low sintering temperatures. Thus, materials having a wide variety of properties and various sintering temperatures can be employed without restriction. In particular, use of a low-temperature sinterable ceramic material facilitates one-shot sintering with a low-melting-point metal having low resistivity, such as copper, silver, or gold, and the formation of a ceramic multi-layer substrate having superior high-frequency characteristics.
In recent years, passive elements, such as capacitors and inductors, have been built into a ceramic multi-layer substrates in an attempt to further miniaturize modules. In such a case, the built-in passive elements must have characteristics, which are comparable to or better than those of surface-mounted elements, to maintain the advantages of the miniaturization of the modules.
When passive elements are mounted in a ceramic multi-layer substrate, a substrate material is generally selected so that the passive elements exhibit adequate properties. For example, a dielectric layer having a high dielectric constant is provided at a portion where a capacitor is to be formed, whereas an insulating layer having a high insulating property is provided at other portions so as to obtain a compact and high-performance ceramic multi-layer substrate.
Japanese Examined Patent Application Publication No. 6-8209, assigned to the same assignee as that of the present application, discloses a dielectric ceramic composition represented by the formula Ba(ZrxZnyTaz)xcex1Ow, wherein, on a molar basis, 0.01xe2x89xa6xxe2x89xa60.06, 0.29xe2x89xa6yxe2x89xa60.34, 0.60xe2x89xa6zxe2x89xa60.70, x+y+z=1, 1.00 less than xcex1 less than 1.03, and w is an arbitrary number, as a material used in a dielectric layer having a high dielectric constant. This dielectric ceramic composition is obtained by sintering at a temperature of at least 1,500xc2x0 C., and exhibits significantly superior electrical characteristics, such as a high specific dielectric constant, a low resonant frequency temperature coefficient, and a Q value of at least 8,000 at approximately 7 GHz.
This dielectric ceramic composition, however, has an extremely high sintering temperature of at least 1,500xc2x0 C., and thus precludes one-shot sintering with a low-melting-point metal such as silver. When a glass component is added to decrease the sintering temperature, the substrate""s strength is significantly decreased in some cases, compared to alumina substrates, depending on the type and the content of the glass component, or its electrical and temperature characteristics may be significantly deteriorated even if the substrate strength remains high.
When great importance is placed on the substrate strength, the specific dielectric constant of the substrate is decreased, and capacitors having large capacitances are not easily built on the substrate. When these capacitors are built on the substrate, the electrodes of the capacitors occupy a large area on the substrate, and this is disadvantageous for miniaturization and high-density mounting of the substrate. When great importance is placed on electrical and temperature characteristics, the mechanical strength of the substrate is too low to mount semiconductor devices.
Accordingly, the present invention addresses the foregoing problems by providing a dielectric ceramic composition which can be sintered at a low temperature and which exhibits a high dielectric constant and superior electrical and temperature characteristics, and a ceramic electronic component using the dielectric ceramic composition.
The present invention relates to a dielectric ceramic composition comprising:
a dielectric ceramic component represented by the formula: Ba(ZrxZnyTaz)xcex1Ow, wherein, on a molar basis, 0.01xe2x89xa6xxe2x89xa60.06, 0.29xe2x89xa6yxe2x89xa60.34, 0.60xe2x89xa6zxe2x89xa60.70, x+y+z=1, 1.00 less than xcex1 less than 1.03, and w is an arbitrary number, wherein xcex1 is a molar ratio of ZrxZnyTaz to Ba; and
a glass component comprising silicon oxide and boron oxide.
Preferably, the content of the glass component is 1 to 25 parts by weight with respect to 100 parts by weight of the dielectric ceramic component.
Preferably, the glass component comprises 10 to 60 percent by weight of silicon oxide, 5 to 40 percent by weight of boron oxide, 0 to 30 percent by weight of aluminum oxide, 20 to 70 percent by weight of at least one of an alkaline earth metal oxide and zinc oxide, and 0 to 15 percent by weight of alkali metal oxide.
In the present invention, 30 percent or less by mole of the Zn element in the dielectric ceramic component may be replaced with Ni.
Also 30 percent or less by mole of the Ta element in the dielectric ceramic component may be replaced with Nb.
The present invention also relates to a ceramic electronic component comprising a dielectric layer and a conductive layer, the dielectric layer comprising the above-mentioned dielectric ceramic composition.
In the ceramic electronic component, the conductive layer preferably comprises at least one conductive material selected from a copper-based material, a silver-based material, and a gold-based material.
As described above, the dielectric ceramic composition in accordance with the present invention comprises the dielectric ceramic component represented by the above formula (hereinafter referred to as xe2x80x9cBa(ZrxZnyTaz)xcex1Ow dielectric ceramic componentxe2x80x9d) and the glass component containing at least silicon oxide and boron oxide (hereinafter referred to as the xe2x80x9cSiO2xe2x80x94B2O3 glass componentxe2x80x9d). The dielectric ceramic composition maintains a high specific dielectric constant, a small-resonant frequency temperature coefficient, and a high Q value in a high-frequency region of the Ba(ZrxZnyTaz)xcex1Ow dielectric ceramic component. Moreover, the dielectric ceramic composition having superior electrical and temperature characteristics is obtainable at a sintering temperature which is lower than melting points of low-melting-point metals.
In the ceramic electronic component having the conductive layer on the dielectric layer, the dielectric layer is formed of the dielectric ceramic composition in accordance with the present invention. Thus, the dielectric layer can be simultaneously sintered together with a low-melting-point metal material having small specific resistance. As a result, the ceramic electronic component exhibits superior electrical and temperature characteristics, and in particular, exhibits superior high-frequency characteristics.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.